Forensic bitemark identification: weak foundations, exaggerated claims

Abstract

Several forensic sciences, especially of the pattern-matching kind, are increasingly seen to lack the scientific foundation needed to justify continuing admission as trial evidence. Indeed, several have been abolished in the recent past. A likely next candidate for elimination is bitemark identification. A number of DNA exonerations have occurred in recent years for individuals convicted based on erroneous bitemark identifications. Intense scientific and legal scrutiny has resulted. An important National Academies review found little scientific support for the field. The Texas Forensic Science Commission recently recommended a moratorium on the admission of bitemark expert testimony. The California Supreme Court has a case before it that could start a national dismantling of forensic odontology. This article describes the (legal) basis for the rise of bitemark identification and the (scientific) basis for its impending fall. The article explains the general logic of forensic identification, the claims of bitemark identification, and reviews relevant empirical research on bitemark identification—highlighting both the lack of research and the lack of support provided by what research does exist. The rise and possible fall of bitemark identification evidence has broader implications—highlighting the weak scientific culture of forensic science and the law's difficulty in evaluating and responding to unreliable and unscientific evidence.

Bite Mark Analysis in Foodstuffs and Inanimate Objects and the Underlying Proofs for Validity and Judicial Acceptance

“…We do not agree with the pessimistic position of Saks et al (46) when declaring the "impeding fall of bite mark evidence," as they themselves limit the criminal context only to the finding of bite marks in the substrate skin. As we have seen, there are a large number of studies and cases of other substrates that offer the possibility of recording the dental pattern more reliably.…”

“…This statement is emphatically reaffirmed by Saks et al, who added in a very recent article (46) that "careful research would need to be designed in order to isolate the various possible causes of the errors and to try to develop ways to reduce errors stemming from those causes." We agree with the authors that this should be applicable to both false positives and false negatives, so that forensic scientists (beyond their expected depositions at trial) should make explicit in their research results not only the error rates but also the most demanded claim made by the scientific community: the validation of a field's technique, still absent in bite mark identification (46). Specifically in the field of bite mark analysis in foodstuffs and inanimate objects, we consider that publications (the obvious result of scientific research), still lack error rates and validated methodologies, and we believe that they are keys factors in solving the equation.…”

“…In particular, although the presence of an explicit known or potential error rate—the ruling (c) —may be simple to verify in a published document, the NAS stated that bite mark testimony has been “introduced in criminal trials without any meaningful scientific validation, determination of error rates, or reliability testing to explain the limits of the discipline” . As far beyond that the concept of “error” can be confusing or even misused both in courtrooms and in forensic research, we agree with Christensen et al in that “as forensic scientists, we must concerned with the clarity, reliability, and validity of our methods.” This statement is emphatically reaffirmed by Saks et al, who added in a very recent article that “careful research would need to be designed in order to isolate the various possible causes of the errors and to try to develop ways to reduce errors stemming from those causes.” We agree with the authors that this should be applicable to both false positives and false negatives, so that forensic scientists (beyond their expected depositions at trial) should make explicit in their research results not only the error rates but also the most demanded claim made by the scientific community: the validation of a field's technique, still absent in bite mark identification . Specifically in the field of bite mark analysis in foodstuffs and inanimate objects, we consider that publications (the obvious result of scientific research), still lack error rates and validated methodologies, and we believe that they are keys factors in solving the equation.…”

Selection of test bites records as part of a forensic bite mark analysis protocol

“…Bite mark comparison is often used in criminal prosecutions; however, the bite mark testimony continues to be criticized for lacking scientific studies that support this type of assessment (Committee 2009). Both the uniqueness of the human dentition and the possibility of the dentition transferring to the bitten substrate (with all possible distortion possibilities) are still basic problems inherent in bite mark analysis and interpretation (Committee 2009;Saks et al 2016). Page et al (2011) stated that "uniqueness is impossible to prove" and added "(mistakes and misidentifications) are made because of guesswork, poor performance, lack of standards, bias and observer error".…”

Exploring the degrees of distortion in simulated human bite marks

“…In the 1970s, research about human tooth shape variability has occurred in superficial attempts and 'uniqueness' became confirmed in court room statements by dentists [4]. Another reasons for uncertainty about 'the value and scientific validity of comparing and identifying bite marks' are the unsatisfactory nature of skin as a substrate for registration of tooth impressions (primary distortion) and also the posture of the body (secondary distortion) [5][6][7]. Several biomechanical properties of the skin contribute to the distortion including nonlinearity and viscoelasticity which vary according to the underlying tissue, adherence to musculature, and anatomic location [8].…”